NOTE phpBB 3.2.x now comes supplied with reCAPTCHA 2 built-in. You should use the built-in version. People supporting older boards (until 3.1.x is out of support) may still want to use the v1.0.4 release of this extension to get reCAPTCHA 2.
This is not official phpBB software. It seems to work for me, but your mileage may vary, and I give no guarantees!